On-board fluid machine

ABSTRACT

An on-board fluid machine includes a housing configured to allow fluid to flow into the housing, an electric motor accommodated in the housing, and a driver that is supplied with DC power and drives the electric motor. The driver includes a low-pass filter circuit and an inverter circuit. The low-pass filter circuit includes a common mode choke coil and a capacitor. The driver further includes a damping unit located at a position where magnetic field lines produced by the common mode choke coil generate eddy current.

BACKGROUND ART

The present invention relates to an on-board fluid machine.

Japanese Laid-Open Patent Publication No. 2010-156271 discloses anon-board fluid machine including, for example, an electric motor and adriver that drives the electric motor. The driver converts DC power,which is supplied from a DC power supply mounted on the vehicle, to ACpower.

Common mode noise and normal mode noise may both be mixed in the DCpower supplied to the driver. In such a case, the noises may interferewith the driver that drives the electric motor. This will affect theoperation of the on-board fluid machine.

In particular, normal mode noise has a frequency that differs inaccordance with the model of the vehicle on which the on-board fluidmachine is mounted. It is thus preferred that the normal mode noise bedecreased over a wide frequency range so that the on-board fluid machinecan be applied to many vehicle models. It is also preferred that this berealized without enlarging the on-board fluid machine.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an on-board fluidmachine that reduces the common mode noise and normal mode noiseincluded in the DC power supplied to the driver.

To achieve the above object, one aspect of the present invention is anon-board fluid machine including a housing, an electric motor, and adriver. The housing is configured to allow fluid to flow into thehousing. The electric motor is accommodated in the housing. The driveris supplied with DC power and drives the electric motor. The driverincludes a low-pass filter circuit and an inverter circuit. The low-passfilter circuit is configured to reduce common mode noise and normal modenoise that are included in the DC power. The inverter circuit isconfigured to convert the DC power, from which the common mode noise andthe normal mode noise have been reduced, to AC power. The low-passfilter circuit includes a common mode choke coil and a capacitor. Thecommon mode choke coil includes a ring core and a first coil and asecond coil that are wound around the ring core. The capacitor iselectrically connected to the common mode choke coil. The driver furtherincludes a damping unit located at a position where magnetic field linesproduced by the common mode choke coil generate eddy current. Thedamping unit is configured to change a frequency characteristic of aphase difference of the common node choke coil. The low-pass filtercircuit has a resonant frequency that is set to a value in a frequencyrange in which the phase difference of the common mode choke coil hasbeen decreased by the damping unit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an on-board motor-driven compressor;

FIG. 2 is an exploded perspective view of a driver;

FIG. 3 is an exploded perspective view of a common mode choke coil andtwo parts;

FIG. 4 is a front view of a ring core around which two coils are wound;

FIG. 5 is an exploded perspective view of the driver;

FIG. 6 is a front view of the common mode choke coil accommodated in adamping unit;

FIG. 7 is a cross-sectional view of the driver corresponding to line 7-7in FIG. 6;

FIG. 8 is a circuit diagram of the driver and an electric motor;

FIG. 9 is a graph illustrating the frequency characteristics of the gainof a low-pass filter circuit;

FIG. 10 is a graph illustrating the frequency characteristics of thephase difference of the common mode choke coil; and

FIG. 11 is a cross-sectional view of a damping unit in a modifiedexample.

EMBODIMENTS OF THE INVENTION

One embodiment of an on-board fluid machine will now be described. Theon-board fluid machine of the present embodiment is an on-boardmotor-driven compressor including a compression unit that compressesfluid. The on-board motor-driven compressor is used with an on-boardair-conditioner. Thus, the compression subject of the on-boardmotor-driven compressor in the present embodiment is a refrigerant.

As shown in FIG. 1, an on-board air-conditioner 200 includes an on-boardmotor-driven compressor 10 and an external refrigerant circuit 201 thatsupplies the on-board motor-driven compressor 10 with a refrigerantserving as a fluid. The external refrigerant circuit 201 includes, forexample, a heat exchanger, an expansion valve, and the like. Theon-board air-conditioner 200 cools or warms the passenger compartmentusing the on-board motor-driven compressor 10 to compress therefrigerant and the external refrigerant circuit 201 to exchange heatwith the refrigerant and expand the refrigerant.

The on-board air-conditioner 200 includes an air-conditioning ECU 202that controls the entire on-board air-conditioner 200. Theair-conditioning ECU 202 is configured to acknowledge the settemperature or the like of the on-board air-conditioner 200. Based onsuch parameters, the air-conditioning ECU 202 sends various commands,such as ON/OFF commands, to the on-board motor-driven compressor 10.

The on-board motor-driven compressor 10 includes a housing 11. Thehousing 11 includes a suction port 11 a. Refrigerant is drawn from theexternal refrigerant circuit 201 through the suction port 11 a.

The housing 11 is formed from a thermally conductive material (e.g.,metal such as aluminum). The housing 11 is connected to ground by thebody of the vehicle.

The housing 11 includes a suction housing portion 12 and a dischargehousing portion 13 that are coupled to each other. The suction housingportion 12 is tubular and includes a flat end wall 12 a and a side wall12 b, which extends from the circumferential portion of the end wall 12a toward the discharge housing portion 13. Further, the suction housingportion 12 has an opening faced toward the discharge housing portion 13.The end wall 12 a is, for example, flat, and the side wall 12 b is, forexample, generally tubular. The discharge housing portion 13 is coupledto the suction housing portion 12 and closes the opening of the suctionhousing portion 12. This defines a cavity in the housing 11.

The suction port 11 a is formed in the side wall 12 b of the suctionhousing portion 12. In detail, the suction port 11 a is located in theside wall 12 b of the suction housing portion 12 closer to the end wall12 a than the discharge housing portion 13.

The housing 11 includes a discharge port 11 b from which the refrigerantis discharged. More specifically, the discharge port 11 b is formed inthe discharge housing portion 13 at a location facing toward the endwall 12 a of the discharge housing portion 13.

The on-board motor-driven compressor 10 includes a rotation shaft 21, acompression unit 22, and an electric motor 23 that are accommodated inthe housing 11.

The rotation shaft 21 is rotationally supported by the housing 11. Theaxial direction of the rotation shaft 21 coincides with thethickness-wise direction of the end wall 12 a (i.e., axial direction oftubular side wall 12 b). The rotation shaft 21 is coupled to thecompression unit 22.

The compression unit 22 is located in the housing 11 closer to thedischarge port 11 b than the suction port 11 a (i.e., end wall 12 a).The compression unit 22 rotates the rotation shaft 21 to compress therefrigerant drawn into the housing 11 from the suction port 11 a anddischarge the compressed refrigerant from the discharge port 11 b. Thecompression unit 22 may be of any construction such as that of a scrolltype, a piston type, or a vane type.

The electric motor 23 is located in the housing 11 between thecompression unit 22 and the end wall 12 a. The electric motor 23 rotatesthe rotation shaft 21 in the housing 11 to drive the compression unit22. The electric motor 23 includes, for example, a cylindrical rotor 24that is fixed to the rotation shaft 21 and a stator 25 that is fixed tothe housing 11. The stator 25 includes a tubular stator core 26 andcoils 27 that are wound around the teeth of the stator core 26. Therotor 24 is opposed to the stator 25 in the radial direction of therotation shaft 21. The coils 27 are energized to rotate the rotor 24 andthe rotation shaft 21 and compress refrigerant with the compression unit22.

As shown in FIG. 1, the on-board motor-driven compressor 10 includes adriver 30 and a cover member 31. The driver 30 is supplied with DC powerand drives the electric motor 23. The cover member 31 defines anaccommodation compartment S0 that accommodates the driver 30.

The cover member 31 is formed from a thermally and electricallyconductive, non-magnetic material (e.g., metal such as aluminum).

The cover member 31 is tubular and includes a closed end and an openend. The opening of the open end is faced toward the housing 11, morespecifically, the end wall 12 a of the suction housing portion 12. Theopen end of the cover member 31 is joined with the end wall 12 a of thehousing 11 and fastened to the end wall 12 a by bolts 32. The end wall12 a closes the opening of the cover member 31. The accommodationcompartment S0 is defined by the cover member 31 and the end wall 12 a.

The accommodation compartment S0 is located outside the housing 11 atthe side of the end wall 12 a opposite to the electric motor 23. Thecompression unit 22, the electric motor 23, and the driver 30 are linedin the axial direction of the rotation shaft 21.

A connector 33 is arranged on the cover member 31, and the driver 30 iselectrically connected to the connector 33. The connector 33electrically connects the air-conditioning ECU 202 and the driver 30.Further, the driver 30 is supplied with DC power from an on-boardelectric storage device 203 installed in the vehicle. The on-boardelectric storage device 203 is a DC power supply, such as a rechargeablebattery or a capacitor, installed in the vehicle.

As shown in FIG. 1, the driver 30 includes a circuit board 40, aninverter circuit 41 laid out on the circuit board 40, two connectionlines EL1 and EL2 electrically connected to the connector 33 and theinverter circuit 41, and a low-pass filter circuit 42 arranged on theconnection lines EL1 and EL2.

The circuit board 40 is flat and spaced apart from the end wall 12 a bya predetermined distance in the axial direction of the rotation shaft21. The circuit board 40 includes a board surface 40 a faced toward theend wall 12 a.

As shown in FIG. 2, the circuit board 40 includes terminal holes 40 band wires 40 c that are connected to terminals inserted through theterminal holes 40 b. The wires 40 c each form at least a portion of thetwo connection lines EL1 and EL2. In detail, the wires 40 c are used toelectrically connect the connector 33 to the low-pass filter circuit 42and to electrically connect the low-pass filter circuit 42 to theinverter circuit 41.

The wires 40 c may be formed on the board surface 40 a or on theopposite surface of the board surface 40 a. Alternatively, the wires 40c may be formed in multiple layers. The wires 40 c may be of anystructure. For example, the wires 40 c may be wire patterns formed on orembedded in the board. Alternatively, the wires 40 c may be bars, likebus bars, or be flat.

The first connection line EL1 is electrically connected by the connector33 to a positive terminal of the on-board electric storage device 203and to the inverter circuit 41. The second connection line EL2 iselectrically connected by the connector 33 to a negative terminal of theon-board electric storage device 203 and to the inverter circuit 41. TheDC power supplied from the on-board electric storage device 203 to theconnector 33 is transmitted over the two connection lines EL1 and EL2.

The low-pass filter circuit 42, which is arranged on the two connectionlines EL1 and EL2, is located at the input side of the inverter circuit41. The low-pass filter circuit 42 is configured to receive DC powerfrom the connector 33. The low-pass filter circuit 42 reduces(attenuates) normal mode noise and common mode noise that are includedin the DC power supplied to the driver 30.

Common mode noise is the noise that flows through the two connectionlines EL1 and EL2 in the same direction. Common mode noise may beproduced when, for example, the driver 30 (i.e., on-board motor-drivencompressor 10) and the on-board electric storage device 203 areelectrically connected through a path (e.g., body of vehicle) other thanthe two connection lines EL1 and EL2.

Normal mode noise is noise that has a predetermined frequency and issuperposed on DC current. Further, normal mode noise is noise in whichcurrent momentarily flows through the two connection lines EL1 and EL2in opposite directions. Thus, normal mode noise can be referred to as aninflow ripple component included in the DC power supplied to the driver30. The low-pass filter circuit 42 will be described in detail later.

The inverter circuit 41 is connected by the wires 40 c to the outputside of the low-pass filter circuit 42. The inverter circuit 41 issupplied with the DC power output from the low-pass filter circuit 42,that is, the DC power of which the normal mode noise and common modenoise have been reduced by the low-pass filter circuit 42.

The inverter circuit 41 converts the DC power to AC power. In detail,the inverter circuit 41 is a three-phase inverter including switchingelements Qu1, Qu2, Qv1, Qv2, Qw1, and Qw2 (hereafter simply referred toas the switching elements Qu1 to Qw2). The switching elements Qu1 to Qw2are cyclically activated and deactivated to convert DC power to ACpower.

The inverter circuit 41 is electrically connected by some of the wires40 c and hermetic terminals (not shown) formed in the end wall 12 a tothe coils 27 of the electric motor 23. The AC power converted from DCpower by the inverter circuit 41 is supplied to the coils 27 to drivethe electric motor 23.

In the present embodiment, the inverter circuit 41 is located betweenthe board surface 40 a and the end wall 12 a. Instead, the invertercircuit 41 may be located at the opposite side of the board surface 40 aor beside the circuit board 40.

The configuration of the low-pass filter circuit 42 will now bedescribed in detail with reference to FIGS. 1, 2 and 3 to 7. Tofacilitate illustration, the low-pass filter circuit 42 is shown withoutan insulator 111 in FIG. 3.

Referring to FIG. 3, the low-pass filter circuit 42 includes a commonmode choke coil 50. The common mode choke coil 50 includes a looped ringcore 51. The ring core 51 of the present embodiment is rectangular andincludes rounded corners so as to be looped (ring-shaped) in an axialview of the ring core 51. Further, the ring core 51 includes two longsides 61 and 71 (extensions), extending straight in a longitudinaldirection in the axial view of the ring core 51, and two short sides 62and 72, extending straight in a lateral direction in the axial view ofthe ring core 51.

The two long sides 61 and 71 are opposed to each other, and the twoshort sides 62 and 72 are opposed to each other. The opposing directionof the two long sides 61 and 71 is orthogonal to the opposing directionof the two short sides 62 and 72.

To aid understanding, the opposing direction of the long sides 61 and 71will be referred to as the X-axis direction, the opposing direction ofthe two short sides 62 and 72 will be referred to as the Y-axisdirection, and the axial direction of the ring core 51 will be referredto as the Z-axis direction. The X-axis direction may also be referred toas the lateral direction of the ring core 51 or the extending directionof the two short sides 62 and 72. The Y-axis direction may be referredto as the longitudinal direction of the ring core 51 or the extendingdirection of the two long sides 61 and 71. The X-axis direction, theY-axis direction, and the Z-axis direction are orthogonal to oneanother.

In the present embodiment, as shown in FIGS. 1 and 2, the Z-axisdirection, which is the axial direction of the ring core 51, coincideswith the axial direction of the rotation shaft 21. However, the Z-axisdirection does not have to coincide with the axial direction of therotation shaft 21, and the common mode choke coil 50 may be directed inany direction. For example, the X-axis direction or the Y-axis directionmay coincide with the axial direction of the rotation shaft 21.

The ring core 51 includes two first corners 63, located at the two endsof the first long side 61 in the Y-axis direction, and two secondcorners 73 located at the two ends of the second long side 71 in theY-axis direction. The two first corners 63 connect the first long side61 to the two short sides 62 and 72. The two second corners 73 connectthe second long side 71 to the two short sides 62 and 72. The corners 63and 73 are each curved and shaped to be sectoral as viewed in the Z-axisdirection.

As shown in FIGS. 3 and 4, the common mode choke coil 50 includes afirst coil 64 and a second coil 74 that are wound around the ring core51.

The first coil 64 is wound around the entire first long side 61, whichincludes a central portion 61 a of the first long side 61 in the Y-axisdirection, and the first corners 63. The first long side 61 and thefirst corners 63 form a first winding portion around which the firstcoil 64 is wound.

The first coil 64 includes a first high-density portion 64 a and firstlow-density portions 64 b. The first high-density portion 64 a has awinding density that differs from that of the first low-density portions64 b. The winding density is the number of windings per unit length inthe winding axis direction. The winding density of the firsthigh-density portion 64 a is higher than the winding density of thefirst low-density portions 64 b.

The first high-density portion 64 a is arranged on and around thecentral portion 61 a of the first long side 61. The first low-densityportions 64 b are arranged at the two opposite sides of the firsthigh-density portion 64 a. More specifically, the first low-densityportions 64 b are arranged on the two ends of the first long side 61 inthe Y-axis direction and on the first corners 63.

Since the first corners 63 are curved, the winding density of the firstcoil 64 wound around the first corners 63 has a tendency to become lowerthan that of the first coil 64 wound around the first long side 61.

The second coil 74 is wound around the entire second long side 71, whichincludes a central portion 71 a of the second long side 71 in the Y-axisdirection, and the second corners 73. The second long side 71 and thesecond corners 73 form a second winding portion around which the secondcoil 74 is wound.

The second coil 74 includes a second high-density portion 74 a andsecond low-density portions 74 b. The second high-density portion 74 ahas a winding density that differs from that of the second low-densityportions 74 b. The winding density of the second high-density portion 74a is higher than the winding density of the second low-density portions74 b.

The second high-density portion 74 a is arranged on and around thecentral portion 71 a of the second long side 71. The second low-densityportions 74 b are arranged at the two opposite sides of the secondhigh-density portion 74 a. More specifically, the second low-densityportions 74 b are arranged on the two ends of the second long side 71 inthe Y-axis direction and on the second corners 73.

Since the second corners 73 are curved, the winding density of thesecond coil 74 wound around the second corners 73 has a tendency tobecome lower than that of the second coil 74 wound around the secondlong side 71.

As shown in FIG. 4, the two coils 64 and 74 are not wound around the twoshort sides 62 and 72. The two short sides 62 and 72 may be referred toas non-winding portions around which the two coils 64 and 74 are notwound. Thus, the short sides 62 and 72 include side surfaces 62 a and 72a around which the two coils 64 and 74 are not wound, respectively. Theside surfaces 62 a and 72 a of the short sides 62 and 72 define the twoouter end surfaces of the ring core 51 in the Y-axis direction.Hereinafter, the side surface 62 a will be referred to as the firstnon-winding side surface 62 a of the first short side 62, and the sidesurface 72 a of the second short side 72 will be referred to as thesecond non-winding side surface 72 a. The two non-winding side surfaces62 a and 72 a intersect (more specifically, are orthogonal) the Y-axisdirection, which is the extending direction of the two long sides 61 and71. In the present embodiment, the two non-winding side surfaces 62 aand 72 a extend in the X-axis direction and the Z-axis direction. Thetwo non-winding side surfaces 62 a and 72 a are opposed to each other inthe Y-axis direction.

In the present embodiment, the first non-winding side surface 62 acorresponds to “the first side surface,” and the second non-winding sidesurface 72 a corresponds to “the second side surface.” Further, in thepresent embodiment, the first long side 61 corresponds to “the firstextension,” and the second long side 71 corresponds to “the secondextension.” The winding axis direction of the first high-density portion64 a is the Y-axis direction and coincides with that of the secondhigh-density portion 74 a.

The two coils 64 and 74 are opposed to each other in the X-axisdirection, which is orthogonal to the Z-axis direction that is the axialdirection of the ring core 51. The extending direction of the two longsides 61 and 71 intersects (preferably, is orthogonal to) the opposingdirection of the two coils 64 and 74 and the axial direction of the ringcore 51.

The two coils 64 and 74 are set to have the same number of windings. Thetwo coils 64 and 74 are wound so that the magnetic flux generated by thecoil 64 and the magnetic flux generated by the coil 74 strengthen eachother when common mode currents, which are currents that flow in thesame direction, flow through the two coils 64 and 74 and so that themagnetic flux generated by the coil 64 and the magnetic flux generatedby the coil 74 cancel each other when normal mode currents, which arecurrents that flow in opposite directions, flow through the two coils 64and 74.

As shown by the single-dashed lines in FIG. 4, some of the magnetic fluxleaks even when normal mode currents flow through the two coils 64 and74. This produces leakage flux Bx (i.e., magnetic field lines) in thecommon mode choke coil 50. Thus, the common mode choke coil 50 has apredetermined inductance with respect to normal mode current. In otherwords, the common mode choke coil 50 has a relatively large impedance(in detail, inductance) with respect to common mode currents and arelatively small impedance with respect to normal mode currents.

The two coils 64 and 74 are not wound around the two short sides 62 and72. Thus, magnetic flux has a tendency to leak from the ring core 51. Asa result, the leakage flux Bx has a tendency to be large compared with astructure in which a coil is wound entirely around the ring core 51.Further, the coils 64 and 74 include the low-density portions 64 b and74 b. Thus, the leakage flux Bx has a tendency to be large compared witha structure in which the coils 64 and 74 are formed by only thehigh-density portions 64 a and 74 a.

As described above, the ring core 51 does not have the form of acircular ring that is free from straight portions. Rather, the ring core51 is non-circular and includes the long sides 61 and 71, the shortsides 62 and 72, and the curved corners 63 and 73. The winding densityof the coils 64 and 74 wound around the corners 63 and 73 has a tendencyto be lower than locations that are straightly formed. In this regard,the shape of the ring core 51 including the long sides 61 and 71, theshort sides 62 and 72, and the curved corners 63 and 73 forms thehigh-density portions 64 a and 74 a and the low-density portions 64 band 74 b.

As shown in FIG. 4, the leakage flux Bx is produced at each of the twocoils 64 and 74 and has the form of a loop extending from one of the twonon-winding side surfaces 62 a and 72 a to the other one of the twonon-winding side surfaces 62 a and 72 a in the Y-axis direction. Theleakage flux Bx has a tendency to concentrate more at the twonon-winding side surfaces 62 a and 72 a, which intersect (in detail,extends orthogonal to) the winding axis direction of the high-densityportions 64 a and 74 a, than the side surfaces of the long sides 61 and71. In the present embodiment, the coils 64 and 74 are wound around thecorners 63 and 73 in addition to the long sides 61 and 71. Thus, theleakage of magnetic flux from the side surfaces of the corners 63 and 73is limited, and the leakage flux Bx has a tendency to concentrate at thetwo non-winding side surfaces 62 a and 72 a.

As shown in FIGS. 3 and 5, the common mode choke coil 50 includes afirst input terminal 65, a first output terminal 66, a second inputterminal 75, and a second output terminal 76. The first input terminal65 and the first output terminal 66 extend from the first coil 64. Thesecond input terminal 75 and the second output terminal 76 extend fromthe second coil 74. The terminals 65, 66, 75, and 76 are located at theinner side of the ring core 51 and extend in the Z-axis direction. Inthe present embodiment, the two input terminals 65 and 75 are locatedcloser to the central part of the common mode choke coil 50 than thefirst non-winding side surface 62 a, and the two output terminals 66 and76 are located closer to the central part of the common mode choke coil50 than the second non-winding side surface 72 a. As shown in FIG. 5,the terminals 65, 66, 75, and 76 are inserted through the terminal holes40 b of the circuit board 40 and electrically connected to the wires 40c. This couples the common mode choke coil 50 to the circuit board 40.

The two input terminals 65 and 75 are electrically connected by thewires 40 c to the connector 33, and the two input terminals 65 and 75are supplied with DC current from the on-board electric storage device203. The two output terminals 66 and 76 are electrically connected tothe inverter circuit 41 by the wires 40 c.

As shown in FIG. 1, the low-pass filter circuit 42 includes an Xcapacitor 80 that is electrically connected to the common mode chokecoil 50. In the present embodiment, the driver 30 includes two Ycapacitors 81 and 82 in addition to the X capacitor 80.

In the present embodiment, the common mode choke coil 50 and thecapacitors 80 to 82 are located between the board surface 40 a and theend wall 12 a. Instead, at least one of the common mode choke coil 50and the capacitors 80 to 82 may be located on the surface of the circuitboard 40 opposite to the board surface 40 a or beside the circuit board40.

The capacitors 80 to 82 each include a terminal inserted through thecorresponding terminal hole 40 b and fixed to the circuit board 40. Thiscouples the capacitors 80 to 82 to the circuit board 40 in a stateelectrically connected to the common mode choke coil 50 and the invertercircuit 41. The electrical connection to the capacitors 80 to 82 will bedescribed later in detail.

The driver 30 includes a damping unit 90 located at a position where themagnetic field lines (leakage flux Bx), which are produced by the commonmode choke coil 50, generate eddy current Ie. The location of thedamping unit 90 is set so that the magnetic field lines (leakage fluxBx), which are produced by the common mode choke coil 50, generate eddycurrent Ie at the damping unit 90.

As shown in FIGS. 2 and 3, the damping unit 90 includes a first part 91and a second part 101. The parts 91 and 101 are box-shaped andrespectively include openings 92 and 102, each opening in one direction,and end walls 93 and 103 (bottom walls). The two parts 91 and 101 arearranged with their openings 92 and 102 opposed to each other. Indetail, the two openings 92 and 102 are opposed to each other in theY-axis direction, which is the direction orthogonal to the Z-axisdirection and which intersects (preferably, extends orthogonal to) theX-axis direction. The two parts 91 and 101 cooperate to accommodate thecommon mode choke coil 50. In this case, the two parts 91 and 101 covermost of the common mode choke coil 50.

As shown in FIG. 6, the damping unit 90 (i.e., parts 91 and 101) islocated at a position penetrated by the leakage flux Bx, which isproduced at the common mode choke coil 50, that is, a positionintersecting the leakage flux Bx. The leakage flux Bx penetrates thedamping unit 90 so that the eddy current Ie flows through the dampingunit 90 and generates magnetic flux By in a direction that cancels theleakage flux Bx. The damping unit 90 (i.e., parts 91 and 101) is formedfrom a non-magnetic conductive material, such as aluminum or brass, andhas a relative permeability set to 0.9 to 3.

As shown in FIGS. 6 and 7, the first part 91 includes the first end wall93 (bottom wall) that covers the first non-winding side surface 62 a anda first peripheral wall 94 (side wall) that extends from the first endwall 93 toward the second part 101.

The first end wall 93 is flat and slightly larger than the firstnon-winding side surface 62 a as viewed in the Y-axis direction. Thefirst end wall 93 is opposed to the first non-winding side surface 62 ain the Y-axis direction. In the present embodiment, the first end wall93 corresponds to “the first opposing portion.”

The first peripheral wall 94 is frame-shaped and surrounds the commonmode choke coil 50 as viewed in the Y-axis direction. The firstperipheral wall 94 surrounds both of the two long sides 61 and 71. Thefirst peripheral wall 94 covers substantially one half of the commonmode choke coil 50, that is, the side corresponding to the firstnon-winding side surface 62 a. The first peripheral wall 94 covers theside of each of the two coils 64 and 74 that corresponds to the firstnon-winding side surface 62 a. The first peripheral wall 94 includes afirst distal end 95 that defines the first opening 92.

In the present embodiment, the first end wall 93 is rectangular.Further, the first peripheral wall 94 extends from the edges of thefirst end wall 93 and has the form of a rectangular frame as viewed inthe Y-axis direction. However, the first end wall 93 and the firstperipheral wall 94 may have any form. For example, the first end wall 93may be oval and have the form of an ellipsoid.

As shown in FIG. 5, the first peripheral wall 94 includes a first recess96 that extends from the first distal end 95 toward the first end wall93. The first recess 96 is formed in the first peripheral wall 94 at aportion corresponding to the circuit board 40 and extends from the firstdistal end 95 to an intermediate position in the first peripheral wall94 in the Y-axis direction.

The two input terminals 65 and 75 are extended through the first recess96 and inserted through the terminal holes 40 b. In detail, the twoinput terminals 65 and 75 are extended through the first recess 96toward the circuit board 40 and inserted through the terminal holes 40b. This avoids interference of the two input terminals 65 and 75 withthe first part 91.

As shown in FIGS. 6 and 7, the second part 101 includes the second endwall 103 (bottom wall) that covers the second non-winding side surface72 a and a second peripheral wall 104 (side wall) that extends from thesecond end wall 103 toward the first part 91.

The second end wall 103 and the first end wall 93 are identical inshape. The second end wall 103 is flat and slightly larger than thesecond non-winding side surface 72 a as viewed in the Y-axis direction.The second end wall 103 is opposed to the second non-winding sidesurface 72 a in the Y-axis direction. The first end wall 93 and thesecond end wall 103 are opposed to each other in the Y-axis direction.In the present embodiment, the second end wall 103 corresponds to “thesecond opposing portion.”

The second peripheral wall 104 and the first peripheral wall 94 areidentical in shape. The second peripheral wall 104 is frame-shaped andsurrounds the common mode choke coil 50 as viewed in the Y-axisdirection. The second peripheral wall 104 surrounds both of the two longsides 61 and 71. The second peripheral wall 104 covers substantially onehalf of the common mode choke coil 50, that is, the side correspondingto the second non-winding side surface 72 a. The second peripheral wall104 covers the side of each of the two coils 64 and 74 that correspondsto the second non-winding side surface 72 a. The second peripheral wall104 includes a second distal end 105 that defines the second opening102.

As shown in FIG. 5, the second peripheral wall 104 includes a secondrecess 106 that extends from the second distal end 105 toward the secondend wall 103. The second recess 106 is formed in the second peripheralwall 104 at a portion corresponding to the circuit board 40 and extendsfrom the second distal end 105 to an intermediate position in the secondperipheral wall 104 in the Y-axis direction.

The two output terminals 66 and 76 are extended through the secondrecess 106 and inserted through the terminal holes 40 b. In detail, thetwo output terminals 66 and 76 extend through the second recess 106toward the circuit board 40 and are inserted through the terminal holes40 b. This avoids interference of the two output terminals 66 and 76with the second part 101. Thus, the terminals 65, 66, 75, and 76 of thetwo coils 64 and 74 are extended through one of the two recesses 96 and106 and inserted through the terminal holes 40 b to extend through thecircuit board 40.

As shown in FIG. 7, the driver 30 includes the insulator 111 thatinsulates the common mode choke coil 50 and the damping unit 90. Theinsulator 111 is, for example, an insulation coating, which is appliedto the surface of the common mode choke coil 50, or an insulation film.The insulator 111 functions to prevent short-circuiting between thecommon mode choke coil 50 and the damping unit 90.

The terminals 65, 66, 75, and 76 extend through the insulator 111. Aninsulation coating is applied to the basal ends of the terminals 65, 66,75, and 76 to prevent short-circuiting of the terminals 65, 66, 75, and76 with the two parts 91 and 101.

The insulator 111 is also arranged between the end walls 93 and 103 andthe corresponding non-winding side surfaces 62 a and 72 a. The end walls93 and 103 and the non-winding side surfaces 62 a and 72 a are incontact with the insulator 111. In this case, an opposing distance Y1between the end walls 93 and 103 and the corresponding non-winding sidesurfaces 62 a and 72 a is the same as the thickness of the insulator111.

In the present embodiment, the first peripheral wall 94 and the secondperipheral wall 104 are slightly larger than the common mode choke coil50 as viewed in the Y-axis direction so that the insulator 111 is spacedapart from the two peripheral walls 94 and 104.

However, the insulator 111 may be in contact with the two peripheralwalls 94 and 104. This will allow the heat of the common mode choke coil50 to be transmitted in a preferred manner to the two parts 91 and 101and improve the heat dissipation of the common mode choke coil 50.

The insulator 111 may have any structure. For example, the insulator 111may be an insulation coating applied to the inner surfaces of the twoparts 91 and 101. In FIG. 7, the insulator 111 is illustrated thickerthan actual.

The two parts 91 and 101 are coupled to the common mode choke coil 50from the Y-axis direction and positioned relative to the common modechoke coil 50 in a state in which the end walls 93 and 103 and thenon-winding side surfaces 62 a and 72 a are in contact with theinsulator 111. Consequently, the opposing distance Y1 (thickness ofinsulator 111) is constant. In other words, the two parts 91 and 101 arepositioned relative to the common mode choke coil 50 so that theopposing distance Y1 is constant regardless of dimensional errors of thetwo parts 91 and 101 and the common mode choke coil 50.

The two parts 91 and 101 may be positioned relative to the common modechoke coil 50 by any structure. For example, the structure may involveengagement, fitting, or adhering. Further, the driver 30 may include aclamp that clamps the two parts 91 and 101 in the Y-axis direction. Inthis case, the two parts 91 and 101 are also coupled to the common modechoke coil 50 in a state in which displacement of the two parts 91 and101 is restricted in the Y-axis direction. The clamp may include, forexample, two urging members that urge the two parts 91 and 101 towardeach other.

As shown in FIG. 7, the two parts 91 and 101 are spaced apart from eachother in a state in which the two distal ends 95 and 105 are opposed toeach other in the Y-axis direction. Thus, a gap 112 extends between thefirst distal end 95 and the second distal end 105. The gap 112 extendsover a distance that is greater than the opposing distance Y1 from theend walls 93 and 103 to the corresponding non-winding side surfaces 62 aand 72 a. The damping unit 90 does not cover portions of the two coils64 and 74 corresponding to the gap 112 extending between the two distalends 95 and 105.

The gap 112 and the central portions 61 a and 71 a of the two long sides61 and 71 are located at corresponding positions in the Y-axisdirection. Thus, the damping unit 90 does not cover the sections of thehigh-density portions 64 a and 74 a in the two coils 64 and 74corresponding to the gap 112, that is, the sections of the two coils 64and 74 wound around the central portions 61 a and 71 a of the two longsides 61 and 71. Further, the damping unit 90 does not cover the sectionof the two coils 64 and 74 corresponding to the two recesses 96 and 106.

The first end wall 93 and the first peripheral wall 94 define a firstpart accommodation compartment S1 in the first part 91. Further, thesecond end wall 103 and the second peripheral wall 104 define a secondpart accommodation compartment S2 in the second part 101. The first partaccommodation compartment S1 and the second part accommodationcompartment S2 are opposed to each other in the Y-axis direction. Inthis case, the common mode choke coil 50 is accommodated in the firstpart accommodation compartment S1 and the second part accommodationcompartment S2. That is, the two parts 91 and 101 cooperate with eachother in a state in which the openings 92 and 102 are opposed to eachother in order to accommodate the common mode choke coil 50. In detail,the two parts 91 and 101 accommodate the common mode choke coil 50 fromthe Y-axis direction that extends orthogonal to the Z-axis direction andintersects (in present embodiment, extends orthogonal to) the X-axisdirection, which is the opposing direction of the two coils 64 and 74.

The two parts 91 and 101 of the damping unit 90 are in contact with thehousing 11 (i.e., end wall 12 a) to allow for heat exchange between thedamping unit 90 and the housing 11. This cools the two parts 91 and 101with the housing 11.

The electrical configuration of the electric motor 23 and the driver 30will now be described.

As shown in FIG. 8, the coils 27 of the electric motor 23 form, forexample, a three-phase construction including a u-phase coil 27 u, av-phase coil 27 v, and a w-phase coil 27 w. The u-phase coil 27 u, thev-phase coil 27 v, and the w-phase coil 27 w are connected to oneanother in, for example, a Y connection.

The inverter circuit 41 includes u-phase switching elements Qu1 and Qu2that correspond to the u-phase coil 27 u, v-phase switching elements Qv1and Qv2 that correspond to the v-phase coil 27 v, and w-phase switchingelements Qw1 and Qw2 that correspond to the w-phase coil 27 w. Theswitching elements Qu1 to Qw2 are, for example, power switching elementssuch as insulated gate bipolar transistors (IGBTs). The switchingelements Qu1 to Qw2 include flywheel diodes Du1 to Dw2 (body diodes).

The u-phase switching elements Qu1 and Qu2 are connected to each otherin series by a connection wire, which is connected to the u-phase coil27 u. The series-connected body of the u-phase switching elements Qu1and Qu2 is electrically connected to the two connection lines EL1 andEL2, and the series-connected body is supplied with DC power from theon-board electric storage device 203.

The other switching elements Qv1, Qv2, Qw1, and Qw2 are connected in thesame manner as the u-phase switching elements Qu1 and Qu2 except in thatthe corresponding coil is different. In this case, the switchingelements Qu1 to Qw2 are connected to the two connection lines EL1 andEL2.

The driver 30 includes a controller 113 that controls the switchingelements Qu1 to Qw2. The controller 113 may be, for example, one or morededicated hardware circuits and/or a circuitry realized by one or moreprocessors running on a computer program (software). Each processorincludes a CPU and a memory such as a RAM and a ROM. The memory stores,for example, program codes or commands configured to have the processorexecute various types of processing. The memory, or computer-readablemedium, is any medium that is accessible and usable by a versatile ordedicated computer.

The controller 113 is electrically connected by the connector 33 to theair-conditioning ECU 202 and cyclically activates and deactivates theswitching elements Qu1 to Qw2 based on commands from theair-conditioning ECU 202. In detail, the controller 113 executespulse-width modulation (PWM) control on the switching elements Qu1 toQw2 based on commands from the air-conditioning ECU 202. Morespecifically, the controller 113 uses a carrier signal (carrier wavesignal) and a command voltage signal (comparison subject signal) togenerate a control signal. Then, the controller 113 uses the generatedcontrol signal to control activation and deactivation of the switchingelements Qu1 to Qw2 and convert DC power to AC power.

As shown in the circuit diagram of FIG. 8, the low-pass filter circuit42 is located between the connector 33 and the inverter circuit 41.

The common mode choke coil 50 is arranged on the two connection linesEL1 and EL2. As described above, the common mode choke coil 50 producesthe leakage flux Bx when normal mode current flows. In this regard, thecommon mode choke coil 50 includes the hypothetical normal mode coils L1and L2 in addition to the two coils 64 and 74. More specifically, in anequivalent circuit, the common mode choke coil 50 of the presentembodiment includes the two coils 64 and 74 and the hypothetical normalmode coils L1 and L2. The hypothetical normal mode coils L1 and L2 arerespectively connected in series to the coils 64 and 74.

The X capacitor 80 is arranged in a stage subsequent to the common modechoke coil 50, or at the side corresponding to the inverter circuit 41,and electrically connected to the two connection lines EL1 and EL2. Thecommon mode choke coil 50 and the X capacitor 80 form an LC resonantcircuit. That is, the low-pass filter circuit 42 of the presentembodiment is an LC resonant circuit that includes the common mode chokecoil 50.

The low-pass filter circuit 42 has a cutoff frequency fc set to be lowerthan a carrier frequency fp that is the frequency of the carrier signal.The carrier frequency fp may also be referred to as the switchingfrequency of each of the switching elements Qu1 to Qw2.

The vehicle includes, for example, a PCU (power control unit) 204, whichserves as an on-board device, in addition to the driver 30. The PCU 204uses the DC power supplied from the on-board electric storage device 203to drive a travel motor or the like installed in the vehicle. In thepresent embodiment, the PCU 204 and the driver 30 are connected inparallel to the on-board electric storage device 203, and the on-boardelectric storage device 203 is shared by the PCU 204 and the driver 30.

The PCU 204 includes, for example, a boost converter 205 and a powercapacitor 206. The boost converter 205 includes a boost switchingelement and cyclically activates and deactivates a boost switchingelement to step-up the DC power of the on-board electric storage device203. The power capacitor 206 is connected in parallel to the on-boardelectric storage device 203. Although not illustrated in the drawings,the PCU 204 includes a travel inverter that converts the DC powerstepped-up by the boost converter 205 to drive force that can drive thetravel motor.

Noise generated by the switching of the boost switching element mayenter the driver 30 as normal mode noise. In this case, the normal modenoise includes noise components corresponding to the switching frequencyof the boost switching element. The switching frequency of the boostswitching element differs between vehicle models. Thus, the frequency ofthe normal mode noise differs between vehicle models. Noise componentscorresponding to the switching frequency of the boost switching elementmay include harmonic components in addition to noise components havingthe same frequency as the switching frequency.

The two Y capacitors 81 and 82 are connected to each other in series. Indetail, the driver 30 includes a bypass line EL3 that connects one endof the first Y capacitor 81 and one end of the second Y capacitor 82.The bypass line EL3 is connected to ground by the vehicle body.

A series-connected body of the two Y capacitors 81 and 82 is locatedbetween the common mode choke coil 50 and the X capacitor 80 andelectrically connected to the common mode choke coil 50. The other endof the first Y capacitor 81 is connected to the first connection lineEL1, that is, the section of the first connection line EL1 connectingthe first coil 64 (first output terminal 66) and the inverter circuit41. The other end of the second Y capacitor 82 is connected to thesection of the second connection line EL2 connecting the second coil 74(second output terminal 76) and the inverter circuit 41.

The frequency characteristics of the low-pass filter circuit 42 will nowbe described with reference to FIG. 9. FIG. 9 is a graph illustratingthe frequency characteristics of the gain G (attenuation amount) of thelow-pass filter circuit 42 relative to the entering normal mode noise.The solid line in FIG. 9 illustrates the frequency characteristics whenthe damping unit 90 exists, and the double-dashed line illustrates thefrequency characteristics when the damping unit 90 does not exist. InFIG. 9, the horizontal axis represents the frequency as a logarithm. Thegain G is a parameter indicating the amount that the normal mode noisecan be reduced.

As shown by the double-dashed line in FIG. 9, when the damping unit 90does not exist, the Q factor of the low-pass filter circuit 42 (i.e., LCresonant circuit including common mode choke coil 50 and X capacitor 80)is relatively high. Thus, it is difficult to reduce the normal modenoise at frequencies that are close to the resonant frequency f0 of thelow-pass filter circuit 42. In other words, the normal mode noise has atendency to increase at frequencies close to the resonant frequency f0of the low-pass filter circuit 42.

In this respect, the present embodiment includes the damping unit 90that is located at a position where the eddy current Ie is generated bythe magnetic field lines (the leakage flux Bx) produced at the commonmode choke coil 50. The damping unit 90 is located at a positionpenetrated by the leakage flux Bx. The penetration of the leakage fluxBx generates the eddy current Ie that produces the magnetic flux By in adirection canceling the leakage flux Bx. Thus, the damping unit 90functions to lower the Q factor of the low-pass filter circuit 42.Accordingly, as shown by the solid line in FIG. 9, the Q factor of thelow-pass filter circuit 42 is low. Thus, the low-pass filter circuit 42also decreases normal mode noise at frequencies close to the resonantfrequency f0 of the low-pass filter circuit 42.

The existence of the damping unit 90 lowers the inductance of thehypothetical normal mode coils L1 and L2. Thus, the resonant frequencyf0 of the low-pass filter circuit 42 in the present embodiment isslightly higher than that when there is no damping unit 90.

As shown in FIG. 9, the tolerable value of the gain G required inaccordance with the specification of the vehicle is referred to as thegain Gth. The Q factor of the gain G of the low-pass filter circuit 42that becomes equal to the tolerable gain Gth when the frequency of thenormal mode noise is the same as the resonant frequency f0 is referredto as a specific Q factor. In the present embodiment, the Q factor ofthe low-pass filter circuit 42 is lower than the specific Q factorbecause of the damping unit 90. Thus, the gain G of the low-pass filtercircuit 42 when the frequency of the normal mode noise is the same asthe resonant frequency f0 is smaller than the tolerable gain Gth (largerin absolute value). In other words, the damping unit 90 is configured tolower the Q factor of the low-pass filter circuit 42 from the specific Qfactor.

One speculation of why the Q factor of the low-pass filter circuit 42becomes low because of the damping unit 90 will now be described. Thedescription hereafter is a speculation and does not negate the validityof the damping unit 90.

The magnetic flux By in the direction that cancels the leakage flux Bxfunctions as magnetic resistance to the leakage flux Bx of the commonmode choke coil 50. Thus, the magnetic flux By, which cancels theleakage flux Bx, impedes the flow of normal mode current through thecommon mode choke coil 50, which causes the leakage flux Bx. In thismanner, the magnetic flux By in the direction that cancels the leakageflux Bx functions as a resistance component to the normal mode current.

The leakage flux Bx in the direction that cancels the magnetic flux Byhas a tendency to increase more easily as the eddy current Ie generatedat the damping unit 90 increases. The eddy current Ie generated at thedamping unit 90 has a tendency to increase more easily as the normalmode noise increases. The normal mode noise (normal mode current) has atendency to increase at frequencies close to the resonant frequency f0of the low-pass filter circuit 42. Thus, the magnetic flux By in thedirection that cancels the leakage flux Bx has a tendency to increase atfrequencies close to the resonant frequency f0 of the low-pass filtercircuit 42. Accordingly, the resistance components of the damping unit90 have a tendency to increase at frequencies close to the resonantfrequency f0 of the low-pass filter circuit 42. This decreases the Qfactor of the low-pass filter circuit 42.

The frequency characteristics of a phase difference θ of the common modechoke coil 50 will now be described with reference to FIG. 10. The phasedifference θ of the common mode choke coil 50 is the difference betweenthe phase of the voltage applied to the common mode choke coil 50 andthe phase of the current flowing through the common mode choke coil 50.FIG. 10 is a graph showing changes in the phase difference θ of thecommon mode choke coil 50 relative to changes in the frequency of normalmode noise (normal mode current). In FIG. 10, the horizontal axisrepresents the frequency as a logarithm.

As shown in FIG. 10, the phase difference θ of the common mode chokecoil 50 varies in accordance with the frequency of the normal modenoise. The arrangement of the damping unit 90 on the common mode chokecoil 50 changes the frequency characteristics of the phase difference θof the common mode choke coil 50. That is, the damping unit 90 (twoparts 91 and 101) changes the frequency characteristics of the phasedifference θ of the common mode choke coil 50.

In detail, when the phase difference θ of the common mode choke coil 50in a case in which there is no damping unit 90 is defined as the firstphase difference θx, as shown in the double-dashed line in FIG. 10, thefirst phase difference θx gradually increases as the frequency increasesin a relatively low frequency range. However, the first phase differenceθx is substantially constant and remains high in a relatively highfrequency range.

When the phase difference θ of the common mode choke coil 50 in a casein which the damping unit 90 is used is defined as the second phasedifference θy, the frequency characteristics of the second phasedifference θy is as shown by the solid line in FIG. 10 and plotted alonga curve including a maximum value θm and a minimum value θn. The secondphase difference θy is the same as the first phase difference θx in arelatively low frequency range but smaller than the first phasedifference θx in a relatively high frequency range.

The frequency range in which the second phase difference θy is smallerthan the first phase difference θx is defined as a specific frequencyrange fb. The specific frequency range fb is the frequency range inwhich the phase difference θ of the common mode choke coil 50 isdecreased by the damping unit 90. When the upper limit value of thefrequency range in which the first and second phase differences θx andθy are both the same is defined as the lower limit frequency fb0, thespecific frequency range fb is a frequency range that is greater thanthe lower limit frequency fb0.

The resonant frequency f0 of the low-pass filter circuit 42 is set to avalue in the specific frequency range fb. In detail, the resonantfrequency f0 of the low-pass filter circuit 42 is set to be higher thanthe lower limit frequency fb0. In the present embodiment, the resonantfrequency f0 of the low-pass filter circuit 42 is set to a value that iscloser to a minimum frequency fn corresponding to the minimum value θnthan a maximum frequency corresponding to the maximum value θm.

The present embodiment has the advantages described below.

(1) The on-board motor-driven compressor 10, which serves as theon-board fluid machine, includes the housing 11 that allows refrigerantserving as fluid to flow therein, the electric motor 23 that isaccommodated in the housing 11, and the driver 30 that drives theelectric motor 23 and is supplied with DC power. The driver 30 includesthe low-pass filter circuit 42 and the inverter circuit 41. The low-passfilter circuit 42 reduces (attenuates) the common mode noise and thenormal mode noise included in the DC power. The inverter circuit 41converts the DC power from which the two noises have been reduced by thelow-pass filter circuit 42 to AC power. The low-pass filter circuit 42includes the looped ring core 51, the common mode choke coil 50 thatincludes the two coils 64 and 74 wound around the ring core 51, and theX capacitor 80 electrically connected to the common mode choke coil 50.

The driver 30 further includes the damping unit 90 set at a positionwhere the leakage flux Bx (magnetic field lines) produced at the commonmode choke coil 50 generates the eddy current Ie at the damping unit 90.The damping unit 90 changes the frequency characteristics of the phasedifference θ of the common mode choke coil 50. The resonant frequency f0of the low-pass filter circuit 42 is set to a value in the specificfrequency range fb that is a frequency range in which the damping unit90 decreases the phase difference θ.

The common mode choke coil 50 reduces the common mode noise included inthe DC power supplied to the driver 30. Further, normal mode currentflows through the common mode choke coil 50 and produces the leakageflux Bx. This reduces the normal mode noise with the common mode chokecoil 50 and the low-pass filter circuit 42 including the X capacitor 80that are electrically connected to each other. Accordingly, there is noneed to use a dedicated coil that reduces normal mode noise. Further,the inverter circuit 41 can be supplied with DC power from which commonmode noise and normal mode noise have both been reduced. Thus,enlargement of the driver 30 can be avoided. This limits enlargement ofthe on-board motor-driven compressor 10.

Further, the damping unit 90 lowers the Q factor of the low-pass filtercircuit 42. In detail, the magnetic field lines (leakage flux) at thecommon mode choke coil 50 generate eddy current at the damping unit 90and lower the Q factor of the low-pass filter circuit 42. This reducesthe normal mode noise at frequencies close to the resonant frequency f0of the low-pass filter circuit 42. Thus, the versatility is improvedwhile limiting enlargement of the on-board motor-driven compressor 10.

As described above, when the low-pass filter circuit 42 has a high Qfactor, it will be difficult to reduce the normal mode noise atfrequencies close to the resonant frequency f0 of the low-pass filtercircuit 42. Thus, the low-pass filter circuit 42 that has a high Qfactor will not effectively function on normal mode noise havingfrequencies close to the resonant frequency f0. This may result inerroneous operation of the driver 30 or shorten the life of the low-passfilter circuit 42. Thus, when the Q factor of the low-pass filtercircuit 42 is high, the low-pass filter circuit 42 cannot be applied toa vehicle model that generates normal mode noise having frequenciesclose to the resonant frequency f0. In the present embodiment, thedamping unit 90 lowers the Q factor. This decreases the normal modenoise at frequencies close to the resonant frequency f0. Morespecifically, the resonant frequency f0 of the low-pass filter circuit42 can be included in the frequency range in which the low-pass filtercircuit 42 is able to reduce the normal mode noise, that is, thefrequency range to which the driver 30 is applicable. This widens thefrequency range of the normal mode noise that can be reduced by thelow-pass filter circuit 42 so that the on-board motor-driven compressor10 can be applied to a wide variety of vehicle models.

To decrease the Q factor, for example, a damping resistor may beconnected in series to the common mode choke coil 50. However, a dampingresistor needs to correspond to relatively large currents and is thusrelatively large. This increases the power loss and generated heat.Thus, heat dissipation and the like need to be taken into considerationwhen connecting the damping resistor to the common mode choke coil 50.This may result in enlargement of the on-board motor-driven compressor10.

In the present embodiment, the eddy current Ie is generated at thedamping unit 90. However, the eddy current Ie is smaller than thecurrent that flows through a damping resistor. Thus, the damping unit 90generates a smaller amount of heat. This limits enlargement of theon-board motor-driven compressor 10 and reduces the two types of noisewhile improving the versatility.

The inventors of the present invention have found that that the changein the frequency characteristics of the phase difference θ of the commonmode choke coil 50, which results from the damping unit 90, and thedecrease in the phase difference θ contribute to the effect for loweringthe Q factor of the low-pass filter circuit 42 (hereafter referred to as“the damping effect”). By setting the value of the resonant frequency f0of the low-pass filter circuit 42 in the specific frequency range basedon this observation, the phase difference θ of the common mode chokecoil 50 can be decreased at frequencies close to the resonant frequencyf0.

The resistance component of the damping unit 90 with respect to theleakage flux Bx varies in accordance with the phase difference θ. Morespecifically, the resistance component of the damping unit 90 increasesas the phase difference θ decreases. Thus, the Q factor of the low-passfilter circuit 42 may be further decreased by setting the resonantfrequency f0 to a frequency at which the phase difference θ is small. Inthis regard, the damping unit 90 of the present embodiment sets theresonant frequency f0 to a value in the specific frequency range fb inwhich the phase difference θ is small. This allows the Q factor of thelow-pass filter circuit 42 to be further reduced.

The damping unit 90 has a first characteristic that generates the eddycurrent Ie to lower the Q factor and a second characteristic thatchanges the frequency characteristics of the phase difference θ of thecommon mode choke coil 50. With regard to the second characteristic, thevalue of the resonant frequency f0 can be set in the specific frequencyrange fb to further reduce the Q factor.

The Q factor of the low-pass filter circuit 42 is lowered to reduce thenormal mode noise at frequencies close to the resonant frequency f0.Thus, the damping effect may be referred to as an effect for reducingnormal mode noise at frequencies close to the resonant frequency f0.

(2) The damping unit 90 is located at a position that the leakage fluxBx produced by the common mode choke coil 50 penetrates. The dampingunit 90 is configured so that the penetration of the leakage flux Bxresults in the flow of the eddy current Ie generated by the magneticflux By in the direction canceling the leakage flux Bx. This obtainsadvantage (1).

(3) The two coils 64 and 74 are opposed to each other in the X-axisdirection that is orthogonal to the axial direction of the ring core 51(Z-axis direction). The ring core 51 includes the first non-winding sidesurface 62 a and the second non-winding side surface 72 a that interestthe Y-axis direction, which is orthogonal to both of the Z-axisdirection and the X-axis direction. The damping unit 90 includes thefirst end wall 93, which serves as the first opposing portion opposingthe first non-winding side surface 62 a, and the second end wall 103,which serves as the second opposing portion opposing the secondnon-winding side surface 72 a. In the common mode choke coil 50 in whichthe two coils 64 and 74 are opposed to each other in the X-axisdirection, flux easily leaks from the two non-winding side surfaces 62 aand 72 a, which intersect the Y-axis direction. Thus, the leakage fluxBx has a tendency to concentrate at the two non-winding side surfaces 62a and 72 a. In this regard, the end walls 93 and 103 are opposed to thenon-winding side surfaces 62 a and 72 a in the present embodiment. Thus,the leakage flux Bx easily penetrates the two end walls 93 and 103. Inother words, the amount of the leakage flux Bx that does not penetratethe damping unit 90 can be reduced. Accordingly, the damping effect canbe improved.

(4) The damping unit 90 includes the box-shaped parts 91 and 101. Theparts 91 and 101 include the end walls 93 and 103 and the peripheralwalls 94 and 104, respectively. The peripheral walls 94 and 104 extendfrom the end walls 93 and 103 and are frame-shaped so as to surround thecommon mode choke coil 50 as viewed in the Y-axis direction, which isthe opposing direction of the end walls 93 and 103. The distal ends 95and 105 of the peripheral walls 94 and 104 define the openings 92 and102, respectively. In a state in which the openings 92 and 102 areopposed to each other, the two parts 91 and 101 cooperate to accommodatethe common mode choke coil 50.

The end walls 93 and 103 cover the non-winding side surfaces 62 a and 72a where the leakage flux Bx has a tendency to concentrate. Thus, theleakage flux Bx easily penetrates the two end walls 93 and 103. Further,the leakage flux Bx that penetrates the two end walls 93 and 103generates the eddy current Ie at the peripheral walls 94 and 104. Theeddy current Ie flows in the circumferential direction of theframe-shaped peripheral walls 94 and 104. That is, the eddy current Ieforms a closed loop as viewed in the Y-axis direction. This easily formsthe magnetic flux By in a direction that cancels the leakage flux Bxflowing in the Y-axis direction (i.e., extending direction of first andsecond long sides 61 and 71). Thus, the damping effect can be furtherimproved.

When accommodating the common mode choke coil 50 with the two box-shapedparts, for example, when coupling two parts to the common mode chokecoil 50 from the X-axis direction, the peripheral wall will beframe-shaped as viewed in the X-axis direction and not frame-shaped asviewed in the Y-axis direction. Such a structure limits the generationof the eddy current Ie forming a closed loop at the peripheral wall asviewed in the Y-axis direction. This decreases magnetic flux in thedirection canceling the leakage flux Bx.

In the present embodiment, as described above, the existence of theperipheral walls 94 and 104 that are frame-shaped as viewed in theY-axis direction will easily generate the eddy current Ie that forms aclosed loop at the peripheral walls 94 and 104. This sufficientlygenerates the magnetic flux By in a direction that cancels the leakageflux Bx and further improves the damping effect.

In the present embodiment, the two parts 91 and 101 cooperate toaccommodate the common mode choke coil 50. Thus, in comparison with astructure that accommodates the common mode choke coil 50 with a singlepart, the common mode choke coil 50 can be accommodated in a relativelyeasy manner.

When accommodating the common mode choke coil 50 with a single part, thepart may include an opening so that the common mode choke coil 50 can beinserted from the opening. In this case, the damping unit will notentirely cover a single surface of the common mode choke coil 50. Thiswill adversely affect the Q factor lowering effect (hereafter referredto as the damping effect) of the low-pass filter circuit 42.

For example, when the damping unit has a size that allows for theaccommodation of the entire common mode choke coil 50 and is formed by asingle part including an opening directed in the Y-axis direction andenabling the insertion of the common mode choke coil 50, one of the twonon-winding side surfaces 62 a and 72 a will not be covered by thedamping unit. Thus, it will be difficult for the leakage flux Bx topenetrate the damping unit. Further, for example, when the damping unithas a size that allows for the accommodation of the entire common modechoke coil 50 and is formed by a single part including an openingdirected in the X-axis direction or the Z-axis direction and enablingthe insertion of the common mode choke coil 50, the damping unit willnot be looped and closed as viewed in the Y-axis direction and will beU-shaped and open at one side. This will hinder the flow of the eddycurrent Ie, which forms a closed loop as viewed in the Y-axis direction,through the damping unit. In contrast, the damping unit 90 of thepresent embodiment is formed by the two parts 91 and 101. Thus, theabove problem does not occur.

(5) The peripheral walls 94 and 104 are frame-shaped and do not includegaps or slits as viewed in the Y-axis direction. Thus, the eddy currentIe that flows through the peripheral walls 94 and 104 is not hindered bygaps or slits. This increases the eddy current Ie, which, in turn,increases the damping effect.

(6) The gap 112 is formed between the two distal ends 95 and 105. Thislimits variations in the opposing distance Y1 of the non-winding sidesurfaces 62 a and 72 a from the end walls 93 and 103 caused bydimensional errors of the two parts 91 and 101 and the common mode chokecoil 50. Thus, variations are limited in damping effect of the two parts91 and 101.

More specifically, the damping effect produced by the two parts 91 and101 varies in accordance with the opposing distance Y1 of thenon-winding side surfaces 62 a and 72 a from the end walls 93 and 103.Thus, there is a need to keep the opposing distance Y1 constant in orderto obtain a stable damping effect.

When the two parts 91 and 101 are formed so that the two distal ends 95and 105 are not spaced apart by the gap 112, the two parts 91 and 101can be positioned when the two distal ends 95 and 105 come into contactwith each other. In this case, the opposing distance Y1 may vary becauseof dimensional errors of the two parts 91 and 101 and the common modechoke coil 50.

In the present embodiment, the gap 112 is formed between the two distalends 95 and 105. Thus, the two parts 91 and 101 are not positioned bycontact of the two distal ends 95 and 105. This allows the gap 112 tovary in correspondence with the dimensional errors described above tokeep the opposing distance Y1 constant. Thus, the advantages describedabove can be obtained.

(7) The insulator 111 is located between the end walls 93 and 103 andthe non-winding side surfaces 62 a and 72 a. The two parts 91 and 101are positioned in a state in which the non-winding side surfaces 62 aand 72 a and the end walls 93 and 103 are in contact with the insulator111. This allows the opposing distance Y1 to be decreased and improvesthe damping effect.

(8) The damping unit 90 does not cover the portion of the common modechoke coil 50 corresponding to the gap 112. This may lower the dampingeffect. In this regard, in the present embodiment, the gap 112 islocated at a position corresponding to the central portions 61 a and 71a in the extending direction of the long sides 61 and 71 of the ringcore 51. The central portions 61 a and 71 a of the long sides 61 and 71is where the coils 64 and 74 (i.e., high-density portions 64 a and 74 a)exist. At such portions, the leakage of magnetic flux is limited. Thislimits decreases in the damping effect even if the gap 112 is formedbetween the two distal ends 95 and 105.

(9) The driver 30 is provided with the circuit board 40 that includesthe inverter circuit 41 and the low-pass filter circuit 42. Theperipheral walls 94 and 104 include the recesses 96 and 106 that extendfrom the distal ends 95 and 105 toward the end walls 93 and 103 tointermediate positions of the peripheral walls 94 and 104. The firstinput terminal 65 and the first output terminal 66 that extend from thefirst coil 64 and the second input terminal 75 and the second outputterminal 76 that extend from the second coil 74 are extended through oneof the two recesses 96 and 106 and inserted into the terminal holes 40 bof the circuit board 40. This electrically connects the common modechoke coil 50 and the circuit board 40.

When just electrically connecting the common mode choke coil 50 and thecircuit board 40, the peripheral walls 94 and 104 may include slitsextending from the distal ends 95 and 105 to the end walls 93 and 103.However, when the peripheral walls 94 and 104 includes such slits, itwill be difficult to form a looped that is closed as viewed in theY-axis direction in the two parts 91 and 101. This limits the generationof the eddy current Ie in the two parts 91 and 101. In this regard, inthe present embodiment, the recesses 96 and 106 extend to intermediatepositions of the peripheral walls 94 and 104. Thus, at least theportions of the peripheral walls 94 and 104 corresponding to the side ofthe end walls 93 and 103 have the form of a closed frame. This forms aclosed loop through which the eddy current flows in the peripheral walls94 and 104 and obtains the damping effect.

The portions of the two peripheral walls 94 and 104 at the sidecorresponding to the distal ends 95 and 105 contributes less to thedamping effect than the portions of the two peripheral walls 94 and 104at the side corresponding to the end walls 93 and 103 and the end walls93 and 103 of the two parts 91 and 101. Thus, even when the peripheralwalls 94 and 104 include the recesses 96 and 106, the damping effectdoes not decrease. Accordingly, the common mode choke coil 50 and thecircuit board 40 can be electrically connected while decreasing thedamping effect.

(10) The terminals 65, 66, 75, and 76 are located closer to the centralpart of the common mode choke coil 50 than the two non-winding sidesurfaces 62 a and 72 a. This allows the recesses 96 and 106 to havesmaller dimensions. Thus, the cross-sectional area of the eddy currentIe, which flows in the circumferential direction of the peripheral walls94 and 104, can be increased. This limits decreases in the dampingeffect caused by the recesses 96 and 106.

(11) The inverter circuit 41 includes the switching elements Qu1 to Qw2,and the switching elements Qu1 to Qw2 are PWM-controlled to convert DCpower to AC power. Further, the cutoff frequency fc of the low-passfilter circuit 42 is set to be lower than the carrier frequency fp,which is the frequency of the carrier signal used to PWM-control theswitching elements Qu1 to Qw2. This reduces (attenuates) ripple noise,which results from switching of the switching elements Qu1 to Qw2, withthe low-pass filter circuit 42 and limits the ripple noise that isreleased from the on-board motor-driven compressor 10. Morespecifically, the low-pass filter circuit 42 functions to reduce thenormal mode noise and common mode noise that enters the on-boardmotor-driven compressor 10 during operation of the PCU 204 and functionsto reduce the ripple noise that is released during operation of theon-board motor-driven compressor 10.

When widening the frequency range of the normal mode noise that can bereduced by the low-pass filter circuit 42, the resonant frequency f0 maybe set to be higher than the expected frequency range of the normal modenoise to avoid the occurrence of resonance. However, this will alsoincrease the cutoff frequency fc of the low-pass filter circuit 42.Thus, it will be difficult for the cutoff frequency fc to be lower thanthe carrier frequency fp. Further, a situation in in which the carrierfrequency fp increases as the cutoff frequency fc rises is notpreferable because this will increase the switching loss of theswitching elements Qu1 to Qw2.

In the present embodiment, the damping unit 90 reduces the normal modenoise at frequencies close to the resonant frequency f0. Thus, there isno need to increase the resonant frequency f0 in accordance with theexpected frequency range of the normal mode noise. Accordingly, thecutoff frequency fc can be lower than the carrier frequency fp withoutincreasing the carrier frequency fp in excess. This limits the releaseor ripple noise, which results from the switching of the switchingelements Qu1 to Qw2, from the on-board motor-driven compressor 10,without increasing the power loss of the inverter circuit 41.

(12) The frequency characteristics of the phase difference θ of thecommon mode choke coil 50 changed by the damping unit 90 includes themaximum value θm and the minimum value en. In this configuration, theresonant frequency f0 of the low-pass filter circuit 42 is set to avalue closer to the minimum frequency fn, which corresponds to theminimum value en, than the maximum frequency fm, which corresponds tothe maximum value θm. This decreases the phase difference θ of thecommon mode choke coil 50 at frequencies close to the resonant frequencyf0. Thus, normal mode noise at frequencies close to the resonantfrequency f0 can be reduced in a further suitable manner.

It should be apparent to those skilled in the art that the presentinvention may be embodied in many other specific forms without departingfrom the spirit or scope of the invention. Particularly, it should beunderstood that the present invention may be embodied in the followingforms.

The two parts 91 and 101 may accommodate the common mode choke coil 50from a diagonal direction that extends orthogonal to the Z-axisdirection and intersects both of the X-axis direction and the Y-axisdirection. The two parts 91 and 101 may also accommodate the common modechoke coil 50 from the Z-axis direction or from the X-axis direction.The opposing direction in which the openings 92 and 102 oppose eachother is not limited to the Y-axis direction and may be any direction.

The first coil 64 does not have to be wound around the first corners 63and may be wound around only the first long side 61. It is onlynecessary that at least a portion of the first coil 64 be wound aroundthe first long side 61. The same applies to the second coil 74.

The first coil 64 may be wound around the first short side 62 instead ofthe first long side 61. In the same manner, the second coil 74 may bewound around the second short side 72 instead of the second long side71. In this case, the two parts of the damping unit may be coupled tothe common mode choke coil 50 from the X-axis direction.

The two coils 64 and 74 may be wound around the entire ring core 51.More specifically, the non-winding portions around which the coils arenot wound may be omitted from the ring core 51. In other words, the twocoils 64 and 74 may be wound around the side surfaces 62 a and 72 a ofthe short sides 62 and 72 that are planes intersecting the Y-axisdirection, which is orthogonal to both of the axial direction of thering core 51 and the opposing direction of the two coils 64 and 74. Inthis case, the leakage flux Bx has a tendency to concentrate at the sidesurfaces 62 a and 72 a.

The ring core 51 may be circular and formed without the corners 63 and73. In this case, the winding density of the two coils 64 and 74 may befixed. That is, the coils 64 and 74 do not necessarily have to includeboth of the high-density portions 64 a and 74 a and the low-densityportions 64 b and 74 b.

The end walls 93 and 103 and the peripheral walls 94 and 104 may includegaps, slits, or through holes. Further, the two parts 91 and 101 may beat least partially meshed, recessed, embossed, or holed. In this manner,the peripheral walls 94 and 104 do not need to have the form of acompletely closed frame.

The two parts 91 and 101 are identical in shape. Instead, for example,the two peripheral walls 94 and 104 may have different dimensions in theY-axis direction.

The two parts 91 and 101 may include overlapping portions. For example,the distal ends 95 and 105 of the two parts 91 and 101 may be overlappedwith each other. In this case, the peripheral wall of one of the twoparts 91 and 101 may be larger than that of the other one so that thetwo distal ends 95 and 105 do not abut against each other. Thus, the gap112 is not necessary.

The gap 112 does not have to be located at a position corresponding towhere the central portions 61 a and 71 a of the long sides 61 and 71 arelocated in the Y-axis direction and may be located closer to the centralportions 61 a and 71 a than the two non-winding side surfaces 62 a and72 a or any other position.

Instead of the recesses 96 and 106, the end walls 93 and 103 or theperipheral walls 94 and 104 may include through holes. In this case, theterminals 65, 66, 75, and 76 may be extended through the through holesand inserted through the terminal holes 40 b of the circuit board 40.Further, the recesses 96 and 106 may be omitted, and the terminals 65,66, 75, and 76 may be extended through the gap 112.

The non-winding side surfaces 62 a and 72 a and the end walls 93 and 103do not have to be in contact with the insulator 111. For example, thenon-winding side surfaces 62 a and 72 a may be spaced apart from theinsulator 111. Alternatively, the end walls 93 and 103 may be spacedapart from the insulator 111.

As shown in FIG. 11, a damping unit 120 may be defined by two extendedportions 121 and 122 extending from the housing 11 (i.e., end wall 12 a)toward the circuit board 40. In the same manner as the housing 11, thetwo extended portions 121 and 122 are formed from a non-magneticconductive material (e.g., aluminum) and formed integrally with thehousing 11.

The two extended portions 121 and 122 are opposed to each other in theY-axis direction. The first extended portion 121 is opposed to the firstnon-winding side surface 62 a. The insulator 111 is located between thefirst extended portion 121 and the first non-winding side surface 62 a.Further, the first extended portion 121 and the first non-winding sidesurface 62 a are in contact with the insulator 111. The second extendedportion 122 is opposed to the second non-winding side surface 72 a. Theinsulator 111 is located between the second extended portion 122 and thesecond non-winding side surface 72 a. Further, the second extendedportion 122 and the second non-winding side surface 72 a are in contactwith the insulator 111. The non-winding side surfaces 62 a and 72 a arecovered by the extended portions 121 and 122. In this case, the fluxleakage Bx penetrates the two extended portions 121 and 122 andgenerates the eddy current Ie that interferes with the leakage flux Bxat the extended portions 121 and 122. This lowers the Q factor of thelow-pass filter circuit 42 and changes the frequency characteristics ofthe phase difference θ of the common mode choke coil 50 to obtain thespecific frequency range fb. Thus, advantage (1) is obtained. In thismanner, the damping unit 90 does not need the peripheral walls 94 and104, and the two parts do not have to be box-shaped.

The parts 91 and 101 may be tubular and formed without the end walls 93and 103. The leakage flux Bx partially penetrates the two parts 91 and101. Nevertheless, it is preferred that the parts 91 and 101 include theend walls 93 and 103 in order to increase the damping effect.

The damping unit may include a coupling portion that couples the twoparts 91 and 101. In other words, the damping unit does not have to beformed by two parts and may be formed by a single part. In this case,the damping unit preferably includes an opening that allows for theinsertion of the common mode choke coil 50. Nevertheless, it ispreferred that the damping unit be formed by at least two parts so thatthe common mode choke coil 50 can easily be accommodated in the dampingunit.

The cover member 31 does not need to have a tubular shape. For example,when the suction housing portion 12 includes an annular rib extendingfrom the end wall 12 a in a direction opposite to the side wall 12 b,the cover member 31 may be coupled to the suction housing portion 12 ina state contacting the rib. In this case, the end wall 12 a, the rib,and the cover member 31 define the accommodation compartment S0. In thismanner, the accommodation compartment S0 may be defined by anystructure.

The ring core 51 may have any shape and be, for example, a UU core, anEE core, or a toroidal core. The ring core 51 does not need to have theform of a completely closed ring and may include a gap.

The circuit configuration of the low-pass filter circuit 42 is notlimited to that of the above embodiment. For example, the low-passfilter circuit 42 may include two X capacitors 80. Further, the low-passfilter circuit may be of any type such as a n-type or a T-type.

The Y capacitors 81 and 82 may be omitted. That is, the driver 30 doesnot necessarily have to include Y capacitors. Nevertheless, it ispreferable that the Y capacitors be included since common noise can bereduced in a suitable manner.

The boost converter 205 may be omitted. In this case, the normal modenoise is, for example, noise resulting from the switching frequency ofswitching elements of a travel inverter.

The on-board device is not limited to the PCU 204 and may be any deviceincluding a switching element that is cyclically activated anddeactivated. For example, the on-board device may be an inverter or thelike that is separate from the driver 30.

The on-board motor-driven compressor 10 is of an inline type but insteadmay be of, for example, a camelback type in which the driver 30 isarranged on the outer side of the housing 11 in the radial direction ofthe rotation shaft 21. In this manner, the driver 30 may be located atany location.

The on-board motor-driven compressor 10 is used with the on-boardair-conditioner 200. Instead, for example, when a fuel cell is installedin a vehicle, the on-board motor-driven compressor 10 may be used withan air supply device that supplies air to the fuel cell. In this manner,the compressed subject is not limited to refrigerant and may be anyfluid such as air.

The on-board fluid machine is not limited to the on-board motor-drivencompressor 10 that includes the compression unit 22 and may be anydevice. For example, when the vehicle provided with the on-board fluidmachine is a fuel cell vehicle, the on-board fluid machine may be anon-board electric pump that supplies hydrogen to the fuel cell.

The modified examples may be combined with each other or with the aboveembodiment.

One aspect that can be acknowledged from the above embodiment and themodified examples will now be described.

(A) An on-board fluid machine including:

a housing configured to allow fluid to flow into the housing;

an electric motor accommodated in the housing; and

a driver that is supplied with DC power and drives the electric motor,wherein the driver includes

-   -   a low-pass filter circuit configured to reduce common mode noise        and normal mode noise that are included in the DC power, and    -   an inverter circuit configured to convert the DC power, from        which the common mode noise and the normal mode noise have been        reduced, to AC power, wherein    -   the low-pass filter circuit includes        -   a common mode choke coil including a ring core and a first            coil and a second coil that are wound around the ring core,            and        -   a capacitor electrically connected to the common mode choke            coil,

wherein the driver further includes a damping unit located at a positionpenetrated by leakage flux that is produced at the common mode chokecoil, the damping unit is configured so that the penetration of theleakage current through the damping unit generates a flow of eddycurrent, and the damping unit changes a frequency characteristic of aphase difference of the common mode choke coil, and a resonant frequencyof the low-pass filter circuit is set in a frequency range in which aphase difference of the common mode choke coil has been decreased by thedamping unit.

The phrase of “the damping unit is configured so that the penetration ofthe leakage current through the damping unit generates a flow of eddycurrent” indicates that, for example, the first part and the second partare formed from a non-magnetic conductive material.

The present examples and embodiments are to be considered asillustrative and not restrictive, and the invention is not to be limitedto the details given herein, but may be modified within the scope andequivalence of the appended claims.

The invention claimed is:
 1. An on-board fluid machine comprising: ahousing configured to allow fluid to flow into the housing; an electricmotor accommodated in the housing; and a driver that is supplied with DCpower and drives the electric motor, wherein the driver includes alow-pass filter circuit configured to reduce common mode noise andnormal mode noise that are included in the DC power, and an invertercircuit configured to convert the DC power, from which the common modenoise and the normal mode noise have been reduced, to AC power, whereinthe low-pass filter circuit includes a common mode choke coil includinga ring core and a first coil and a second coil that are wound around thering core, and a capacitor electrically connected to the common modechoke coil, the driver further includes a damping unit located at aposition where magnetic field lines produced by the common mode chokecoil generate eddy current, and wherein the damping unit is configuredto change a frequency characteristic of a phase difference of the commonnode choke coil, and the low-pass filter circuit has a resonantfrequency that is set to a value in a frequency range in which the phasedifference of the common mode choke coil has been decreased by thedamping unit.
 2. The on-board fluid machine according to claim 1,wherein the first coil and the second coil are opposed to each other ina first direction that is orthogonal to an axial direction of the ringcore, the ring core includes a first side surface and a second sidesurface that interest a second direction that is orthogonal to both ofthe axial direction and the first direction, and the damping unitincludes a first opposing portion opposed to the first side surface anda second opposing portion opposed to the second side surface.
 3. Theon-board fluid machine according to claim 2, wherein the damping unitincludes: a box-shaped first part including a first end wall that is thefirst opposing portion and a first peripheral wall that extends from thefirst end wall, wherein the first peripheral wall is frame-shaped andsurrounds the common mode choke coil as viewed in a direction in whichthe first and second opposing portions are opposed to each other, andthe first peripheral wall includes a distal end that is a first distalend defining a first opening; and a box-shaped second part including asecond end wall that is the second opposing portion and a secondperipheral wall that extends from the second end wall, wherein thesecond peripheral wall is frame-shaped and surrounds the common modechoke coil as viewed in the direction in which the first and secondopposing portions are opposed to each other, and the second peripheralwall includes a distal end that is a second distal end defining a secondopening, wherein the first part and the second part cooperate toaccommodate the common mode choke coil in a state in which the firstopening and the second opening are opposed to each other.
 4. Theon-board fluid machine according to claim 3, wherein the first distaland the second distal end are spaced apart by a gap.
 5. The on-boardfluid machine according to claim 4, wherein the ring core includes afirst extension and a second extension extending in the seconddirection, the first coil is at least partially wound around the firstextension, the second coil is at least partially wound around the secondextension, and the gap is located at a position corresponding to centralportions of the first and second extensions in the second direction. 6.The on-board fluid machine according to claim 3, wherein the driverfurther includes an insulator that insulates the common mode choke coiland the damping unit, the first part is positioned in a state in whichthe first side surface and the first end wall are in contact with theinsulator, and the second part is positioned in a state in which thesecond side surface and the second end wall are in contact with theinsulator.
 7. The on-board fluid mechanism according to claim 1, whereinthe frequency characteristic of the phase difference of the common modechoke coil changed by the damping unit includes a maximum value and aminimum value, and the resonant frequency of the low-pass filter circuitis set to a value closer to a minimum frequency corresponding to theminimum value than a maximum frequency corresponding to the maximumvalue.
 8. The on-board fluid machine according to claim 1, wherein thedamping unit is located at a position where leakage flux produced at thecommon mode choke coil penetrates, and the leakage flux penetrates thedamping unit to generate a flow of eddy current.
 9. The on-board fluidmachine according to claim 1, wherein the on-board fluid machine is anon-board motor-driven compressor including a compression unit driven bythe electric motor and configured to compress the fluid that enters thehousing.